The present invention relates to a data slicer circuit for separating and recovering digital teletext signals from the composite color signal demodulated in color-television receivers. More specifically, the present invention pertains to a data slicer circuit wherein a slicing level is derived from the teletext signals with the aid of a framing-code detector and a gating pulse whose active phase is present at least for the duration of the horizontal- and color-sync pulses.
The necessity of such a data slicer circuit is explained in the journal "Funkschau", 1977, pages 820 to 824 and 882 to 887, in an article entitled "Die Grundlagen von Teletext und Viewdata", particularly page 882, right column, to page 884 in connection with FIGS. 15 and 16. The circuit shown in FIG. 16, a "dynamic data slicer", primarily consists of an arrangement for rectifying and storing the peak and valley values of the data current. FIG. 16 shows a rectifier circuit for this purpose which consists of diodes, resistors, and capacitors. FIG. 17 on page 884 shows various waveforms occuring with the European teletext standard. It can be seen that the teletext signals follow the color burst in time. A clock run-in is followed by a framing code with is followed by the actual teletext data signals. FIG. 17 also shows that during the active phase of horizontal-, vertical-, and color-sync pulses (color burst), a gating signal, designated there by Q1, is produced by the circuit.
It is one object of the invention to provide a fully digital data slicer circuit for a digital television receiver, i.e., a circuit which processes the already digitized composite color signal in digital fashion. Digital signal processing into television receivers is known per se from the journal "electronics", Aug. 11, 1981, pages 97 to 103.